Potential Windows Error Manager Masquerading

Attackers may attempt to evade defenses by masquerading malicious processes as legitimate Windows Error Reporting (WER) executables, specifically WerFault.exe or Wermgr.exe. These executables are responsible for handling application crashes and reporting errors to Microsoft. This technique involves launching these executables without command-line arguments and then establishing outgoing network connections. By mimicking the behavior of legitimate WER processes, adversaries can potentially bypass detections that focus on suspicious child process activity or command-line arguments, effectively blending their malicious network activity with normal system operations. This technique has been observed in conjunction with malware campaigns, highlighting the importance of detecting deviations from the expected behavior of WER processes.

Attack Chain

1. An attacker gains initial access to the system through an unspecified method.
2. The attacker deploys a malicious payload onto the compromised system.
3. The attacker executes WerFault.exe or Wermgr.exe without any command-line arguments. This is an attempt to mimic legitimate WER process behavior.
4. The masquerading WER process initiates an outgoing network connection to a command-and-control (C2) server. The specific protocol used is not specified.
5. The C2 server issues commands to the compromised system through the masquerading WER process.
6. The attacker executes malicious commands on the system, potentially including data exfiltration, lateral movement, or further payload deployment.
7. The attacker attempts to maintain persistence on the compromised system, potentially through registry modifications or scheduled tasks.
8. The attacker achieves their final objective, such as data theft, system disruption, or establishing a foothold for future attacks.

Impact

A successful masquerading attack can lead to a prolonged period of undetected malicious activity. Victims may experience data breaches, system compromise, and potential financial losses. The targeted systems could be incorporated into a botnet, used for cryptocurrency mining, or further exploited for lateral movement within the network. The lack of command-line arguments makes detection more challenging, allowing attackers to operate with a lower risk of detection.

Recommendation

• Monitor process creation events for instances of WerFault.exe or Wermgr.exe executed with a single argument and an unusual command line, using the “Potential Windows Error Manager Masquerading” Sigma rule to detect such events.
• Investigate network connections originating from WerFault.exe or Wermgr.exe, especially when the process is launched without arguments.
• Enable Sysmon Event ID 1 (Process Creation) and Event ID 3 (Network Connection) logging to provide the necessary data for the Sigma rule.
• Correlate process creation and network connection events to identify suspicious sequences, as outlined in the attack chain.
• Implement network segmentation to limit the potential impact of compromised systems and restrict lateral movement.